Silicon carbide (SiC) is expected to be used as a material for a next-generation semiconductor device. SiC has the following physical properties: a band gap is three times wider than that of silicon (Si); breakdown field strength is about ten times more than that of Si; and thermal conductivity is about three times more than that of Si. The use of these characteristics makes it possible to achieve a semiconductor device which has low power consumption and can operate at a high temperature.
A trench-gate metal oxide semiconductor field effect transistor (MOSFET) in which a gate electrode is provided in a trench has been known as a structure for reducing an on-resistance of the MOSFET using SiC. In the trench-gate MOSFET, there is a concern that the breakdown of a gate insulating film will occur due to the concentration of the electric field at the bottom of the trench.